Spread of Pseudomonas syringae pv. tomato and Role of Epiphytic Populations and Environmental Conditions in Disease Development. D. R. Smitley, Former Graduate Assistant, Department of Plant Pathology, University of Georgia, Athens 30602. S. M. McCarter, Professor, Department of Plant Pathology, University of Georgia, Athens 30602. Plant Dis. 66:713-717. Accepted for publication 10 November 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-713.

In field plots near Athens, GA, Pseudomonas syringae pv. tomato, which causes bacterial speck of tomato (Lycopersicon esculentum), spread rapidly during the cool and moist growing season of 1979 but failed to spread during 1980 when mild to hot and dry weather occurred. In 1979, numbers of epiphytic bacteria and lesions on foliage of Chico III tomato plants increased rapidly from transplanting in late April until early June but then declined with the onset of low-moisture conditions and mean daily temperatures often above 25 C. Epiphytic populations and lesion development continued to decline at high temperatures in July, although moisture levels were again high. Fruits that developed during cool, moist weather in early season were more severely infected than those that developed later. P. syringae pv. tomato spread rapidly by natural means, and clipping of transplant beds increased disease severity. Although total fruit yields were not significantly reduced by bacterial speck, quality was markedly reduced because 70% of fruit were infected in early harvests. Streptomycin and cupric hydroxide reduced spread and fruit infection. In the growth chamber and field, P. syringae pv. tomato survived as an epiphyte on symptomless tomato plants for extended periods to produce disease under conducive environmental conditions.

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